The present invention relates to a spinning rotor for open-end spinning machines, wherein the rotor has a rotor cup with a collar and is suitable for a high number of rotor revolutions, and relates further to a method for producing such a spinning rotor.
With rapidly rotating bodies, for example spinning rotors, an imbalance occurs when the mass of the body is distributed in such a way that the center of gravity lies outside of the axis of rotation, or if the axis of rotation and the axis of inertia are not coincident. The imbalance results in undesired reaction forces during the rotation of the body causing uneven running or vibrations, which in particular increase considerably as rotational speed increases and/or in certain frequency ranges. Undesired results can occur, for example, loud noises, malfunctions, wear or even destruction of the rotor, which require maintenance or the replacement of such unbalanced components. Expense and downtime are created because of maintenance and replacement work, and the efficiency and/or the productivity, of the machine is negatively affected.
To prevent such disadvantages, dynamic balancing is customarily performed as a portion of the production process of such rapidly rotating bodies. In some cases, the mass equalization of the body can be accomplished by the installation of weights or in most cases by the removal of material from the body.
Presently the operating speed of spinning rotors in open-end spinning machines already is greater than 100,000 rpm. With such high numbers of revolution, the bearings and drive mechanisms of the spinning rotors are exposed to enormous stresses, together with the above described disadvantages, even in cases of small imbalances. It is therefore well known that it is imperative to not only produce spinning rotors with the highest precision in shape, but also to balance them carefully. In accordance with the known prior art, the balancing the spinning rotors by the removal of material is accomplished by grinding its exterior circumference. Grinding is customarily performed on the rotor cup at the end edge of the collar and at the exterior circumference at the location of its greatest circumference. Balancing of this type is known, for example, from European Patent Document EP 0 099 490 B1, as well as German Patent Publication DE 43 12 365 A1.
Balancing, already described as the prior art in European Patent Document EP 0 099 490 B1, is performed by grinding the exterior circumference of the spinning rotor. Although the removal of material as described in this reference has a considerable effect, the relatively thin wall of open-end spinning rotors, particularly in those rotors formed by a non-cutting formation process, is weakened at a critical point. In European Patent Document EP 0 099 490 B1 it is already expressly pointed out that such weakening must be absolutely avoided in view of the high number of rotor revolutions which is customary today. A balancing method is therefore disclosed in this reference wherein a first production step accomplishes mass equalization by initially punching a hole through the bottom of the rotor cup in the course of the compression process, and thereafter the hole may be enlarged to a degree sufficient for mass equalization. Such method, however, is expensive, time-consuming and, in particular, is limited to spinning rotors made by plastic deformation, for example from sheet metal.
German Patent Publication DE 43 12 365 A1 describes a rotor balancing method by grinding of the rotor collar. However, the considerable outlay required in the course of such balancing is disadvantageous.
German Patent Publication DE 43 39 064 A1 discloses a balancing method wherein balancing is performed by means of a pulsating laser beam. The pulse frequency of the laser beam is synchronized with the rotating speed of the rotor within an imbalance measuring device during the balancing process, such that the laser removes material when the unbalanced portion of the rotor turns past the impact point of the laser on the surface of the rotor. However, this method does not operate with sufficient precision for the exact balancing necessary to meet the desired quality requirements to balance the body for operation at high numbers of revolution. The exact guidance of the rotor during the rotating movement in the course of the balancing process is an absolute prerequisite for precise balancing by means of such a method, but is either too inaccurate or extraordinarily elaborate and therefore too expensive.
It is accordingly an object of the present invention to achieve further improvements in regard to the balancing of open-end spinning rotors.
In accordance with the invention, this object is attained by a spinning rotor basically comprising a rotor cup with a collar. The spinning rotor is made suitable for operation at a high number of rotor revolutions in an open-end spinning machine by the formation thereon of at least one identification mark created by the removal of material from a selected exterior surface of the rotor cup or the collar, the identification mark being formed at a selected position on the exterior surface and to a selected removal depth for mass equalization of the spinning rotor.
Such a spinning rotor in accordance with the present invention is distinguished by good balancing qualities. The identification mark is accomplished by a precisely metered removal of material. The increased balancing quality leads to quieter running and thus can improve the functional properties of the spinning rotor, in particular the operational dependability of the spinning rotor, and therefore the productivity of the spinning station. The spinning rotor in accordance with the invention does not require any additional removal of material besides the identification mark, such as an interfering notch or cutout, for example, which can lead to undesired and disadvantageous interference with the boundary layer flow or to an impermissible weakening of the stability of the spinning rotor. It is possible to keep the removal depth extremely slight by distributing the material removal over the entire surface of the identification mark, and it therefore has an advantageous effect on the surrounding airflow at high numbers of revolutions of the spinning rotor. A flow-efficient spinning rotor in accordance with the invention reduces energy consumption, particularly at such high numbers of revolutions, is cost-effective because of the reduction of outlay and time during its production, and in this manner allows a considerable cost savings in connection with the customary design of the open-end spinning machines with a plurality of spinning stations.
The identification mark produced by the removal of material is essentially permanent and easily recognizable. It can be used for identification and/or information. For this purpose the identification mark preferably consists of lettering or a graphic symbol, or alternatively a combination of lettering and a graphic symbol.
Advantageously the identification mark is arranged on the exterior circumference of the collar of the spinning rotor, preferably on a cylinder-shaped section of the collar. At this location the material removal is very effective as a mass equalization, without negatively affecting the air resistance or the stability of the spinning rotor, such as otherwise occurs by the notching of the exterior radius of the largest diameter of the rotor cup in accordance with the prior art. It is thus possible to avoid the material removal at the exterior radius of the greatest diameter of the rotor cup, as well as at the edge of the collar toward the shaft, otherwise customary in the course of balancing methods of the prior art, by the effective positioning of the identification mark on the cylinder-shaped section of the collar. Such a double removal of material, created during balancing by grinding at two axially spaced-apart locations, has heretofore often been considered to be imperative.
According to another aspect of the present invention, a method is provided for producing a spinning rotor of the type described suitable for operation at a high number of rotor revolutions in an open-end spinning machine. Briefly summarized, the method basically comprises the steps of initially forming the spinning rotor in a selected shape having a rotor cup and a collar, determining an imbalance in the spinning rotor and an angular position and a size of the imbalance, determining an amount of material to remove from the spinning rotor for mass equalization thereof to offset the imbalance, and removing material from the spinning rotor for equalization of the mass as a function of the angular position and size of the imbalance. As described, the removal of material comprises forming at least one identification mark on the spinning rotor by removing material from a selected exterior surface of the rotor cup or collar and at a selected position on the exterior surface and to a selected removal depth for mass equalization of the spinning rotor. Advantageously, therefore, the creation of such an identification mark can take place simultaneously with the unavoidable mass equalization balancing process in a single method which achieves a considerable savings in time and makes it possible to remove material in a controlled fashion with extraordinary exactitude.
The material removal preferably is performed by guiding a laser beam over the area of the identification mark to be created, which permits a clean and even design of the form of, and the bottom surface within, the identification mark. To this end, it is preferred that the direction of the laser beam be guided by at least one deflection means, in particular an optical device, which makes the guidance simple and precise. The material removal can be exactly controlled or metered by means of the laser beam, is reproducible and can be performed as an automated process.
The removal depth required to achieve mass equalization is preferably calculated on the basis of the size of the removal surface of the identification mark. In the process, the removal depth is advantageously increased in steps. In this manner, a desired uniform appearance of identical rotor types of the mass-produced spinning rotors is achieved, and the required amount of calculation is clearly reduced, since the calculation can be made simpler and more rapidly.
A further simplification and considerable increase in the speed of the determination of the removal depth is achieved in that the respective relationship of shape, surface and removal depth is stored in look-up tables for different identification marks and balance values. Stepped removal depths in particular make the allocation easier, limit the amount of data to be stored and improve the possibilities of their reuse. In this case, the calculation of the removal depth can be omitted entirely, or at least to a large extent. The determination of the removal depth can be limited to the relationship of shape, surface and removal depth of an identification mark to a determined balance value.
The identification mark is preferably provided at least partially as lettering or as a graphic symbol, and as a result, the number of the symbols to be stored can be limited and manageable. The identification or the information can be stored and called-up by known means or information carriers.
Advantageously, if the output of the laser beam is regularly submitted at predetermined time intervals to a preventive or state-dependent calibration process, and if output deviations from a predetermined command value detected in the course of such calibration are compensated by a regulating process performed by a control device, the output of the laser beam remains constant so that the material removal is always performed under reproducible conditions.
The method of the present invention is particularly advantageous for manufacturing a balanced spinning rotor. In a preferred embodiment, the method includes the steps of initially placing the spinning rotor into a receiver of a balancing device operated by means of a laser beam and causing the spinning rotor to rotate in the receiver. The angular position of the spinning rotor may then be detected via a marker and an imbalance of the spinning rotor is measured while being rotated by the receiver at controlled revolutions. A position and a size of the imbalance is determined via a control unit of the balancing device and the volume of material to be removed is calculated, using spinning rotor-specific values. A position, shape and depth of the identification mark required for mass equalization is determined via the control unit of the balancing device. The spinning rotor is rotated to dispose the imbalance underneath the laser beam and within an effective range of the laser beam, and then, while the spinning rotor is not rotating, the laser beam is projected onto the exterior surface of the spinning rotor at an intensity and for a duration of the laser beam matched to the material to be removed.
The present method may be performed rapidly and dependably, results in spinning rotors of high balance quality, requires only small operating outlays since it can be automated, and has a high degree of reproducibility, without being compromised by manual error sources or inadequacies. The identification mark produced is permanent and can be clearly and unambiguously recognized. In particular, the creation of at least one identification symbol in one work step as part of the inevitable mass equalization during balancing permits a significant reduction of the manufacturing outlay and accomplishes a material removal which can be extremely accurately regulated, thereby to achieve a high degree of balance quality. A spinning rotor produced in this manner has improved operating properties, leads to an increase in the dependability and efficiency of the spinning station, a decrease in costs and an increase in productivity.
Further details, features and advantages of the invention will be understood from the following disclosure with reference to the accompanying drawing figures.